Wednesday, 29 October 2014

Rapid Evolution of Tiny Lizard Is No Darwinian Evolution At All

As used by some of its supporters, evolution is a tricky word in that its meaning seems to evolve (i.e. change) in a single story.

A recent illustration is an article published in the journal Science. Its title gives away the sense it is used: Rapid evolution of a native species following invasion by a congener.

The article features Anolis carolinensis, a lizard that moved higher up in a tree to evade predators. According to Science,

“In recent years, biologists have increasingly recognized that evolutionary change can occur rapidly when natural selection is strong; thus, real-time studies of evolution can be used to test classic evolutionary hypotheses directly. One such hypothesis is that negative interactions between closely related species can drive phenotypic divergence. Such divergence is thought to be ubiquitous, though well-documented cases are surprisingly rare. On small islands in Florida, we found that the lizard Anolis carolinensis moved to higher perches following invasion by Anolis sagrei and, in response, adaptively evolved larger toepads after only 20 generations. These results illustrate that interspecific interactions between closely related species can drive evolutionary change on observable time scales.”

While this is change, it is not the kind of change that gave rise to lizards. Anolis carolinensis might be living higher up in a tree, it might have slightly bigger toepads but it has not evolved – and is not evolving – into something else.

What this Darwinian story lacks is a plausible explanation of the origin of Anolis carolinensis.